The present invention relates to a circuit arrangement for driving a periodic saw-tooth current in a coil, in particular for use in the line output stage for a television receiver, comprising a unidirectionally conductive device connected in parallel with the coil and thyristor connected in parallel wiith a series resonant circuit, the gate of the thyristor being connected to a source of periodic pilot pulses, to render the thyristor conductive during part of the saw-tooth cycle.
Circuits of this type have been known for some time in which advantage is taken of the robust nature and easy firing characteristics of the thyristors.
However, thyristors are known to have two weak points, namely:
High-power quenching means are required for extinguishing the thyristor, and PA1 A certain amount of recovery time is needed from when the current stops until positive voltage is again applied to the anode of the thyristor.
There are two types of known circuits. The first type comprises circuits in which the thyristor is extinguished by a resonant circuit connected in series or parallel to the thyristor, which serves as a one-way switch for "charging" the coil which is then discharged through a diode to restore energy to the supply (see, for example, "I.E.E.E. Transactions on BTR," Nov. 1963, pp 9-22, by S. A. Schwartz and L. L. Ornik). Circuits of this type require four times the normal circulation of reactive energy so that their efficiency is not usually very high.
The second type comprises circuits in which a second thyristor is used to extinguish the first by creating a suitable oscillating current. (See, for example, Italian Pat. No. 812,759). Circuits of this type are complex requiring, among other things, two pilot signals of different phase.